A NEW METHOD FOR PHOTOGRAPHIC PROCESSING OF EMULSIONS UP TO 200 μ THICK

The widespread use of thick-layer emulsions with a high concentration of silver bromide has confronted photographic processing with a whole series of specific requirements, among which the following may be mentioned first of all: uniformity of development through the depth of the emulsion layer, minimal veil (fog), absence of deformations that distort the shape of particle tracks, and strong adhesion of the emulsion to the glass at all stages of processing. Numerous works have been devoted to solving these problems, with the method of “temperature development” receiving the widest use[^1][^2][^3][^4].

The author of the work reviewed[^5] obtained exceptionally clean, uniformly developed plates, free from any distortions of the emulsion layer, which adhered firmly to the glass support. This was achieved as a result of a considerable change in the formula and processing regime in the method of “temperature development.” The principal changes, rationally substantiated by the author, are as follows: preliminary impregnation of the emulsion layer with distilled water is eliminated, as is mechanical mixing of the solutions. Potassium bromide and hydroquinone are excluded from the composition of the developer; the development temperature is lowered \((<20^\circ)\); the concentration of the solution stopping development is reduced; two fixing solutions are introduced, one of which contains a tanning solution. All processing is carried out in a room with conditioned air, the temperature of which may vary from 13 to 20° C. By continuously changing the room temperature during processing, convection currents of the solution around the plate are created, ensuring a uniformity of processing better than with ordinary mechanical stirring.

Formula of the solutions. All solutions are prepared from reagents of high purity in distilled water. Thoroughly cleaned vessels made of glass or stainless steel are used for preparing and storing the solutions. The developer consists of two solutions, which are mixed before use: solution A: metol — 3 g, water — 1000 ml; solution B: Na₂CO₃ (anhydrous) — 50 g, NaHCO₃ — 50 g, water — 1000 ml. Stopping solution: 0.3–0.5% acetic acid. The fixing solutions are prepared from saturated stock (60%) solutions of pure sodium thiosulfate on the day of use. Tanning solution: solution A: Na₂SO₃ (anhydrous) — 32 g, glacial acetic acid (of highest purity) — 50 ml, water — 165 ml; solution B: potassium alum — 70 g, water 840 ml. First fixing solution: cold (15°) water — 300 ml, mixture of tanning solution \((A + B)\) — 50 ml, cold (15°) saturated thiosulfate solution — 320 ml. Second fixing solution: 350 ml saturated thiosulfate solution + 350 ml water.

Procedure: the plates are placed in a cold developer (4°) for 30 min. (if the thickness is 100 $\mu$) or for 40 min. (200 $\mu$). They are then placed on filter paper for 10 min. at 19°C and then transferred to the developer at 17–19°C. The development time ranges from 33 to 56 min., depending on the type of emulsion, the thickness of the layer, and the temperature. Convection currents in the solution are produced by changing the room temperature from 19 to 18.8°C during the first 15–20 min. and from 18.8 to 19°C during the remaining 15–20 min. The plates are then rinsed with filtered distilled water, immersed in a stop bath for 15 min., rinsed again, and placed in the first hardening fixing bath, whose temperature is continuously varied between 15 and 20°C by changing the room temperature. The fixing time is equal to three times the clearing time of the film, i.e., 6 hours for 100-$\mu$ plates and 15 hours for 200-$\mu$ plates. The plates are then transferred to the second fixing bath for the same length of time and with the same temperature fluctuations. This is followed by washing with tap water (5–12 hours) and drying in a horizontal position on filtered paper in a glass cabinet (12–48 hours). Finally, the surface of the dry emulsion should be mechanically cleaned with cotton wool moistened with alcohol. The microphotographs presented in the paper under review demonstrate the exceptionally high quality of the images of tracks in Ilford C2 and G5 emulsions developed by the new method.

A. Kh.

CITED LITERATURE

1. M. Wilson, S. Yanselow, Phys. Rev. 75, 1144 (1949); collection The Photographic Method in Nuclear Physics.
2. C. Dilworth, G. Occhialini, R. Paine, Nature 163, 102 (1948).
3. C. Dilworth, G. Occhialini, L. Vermäesen, Fundamental mechanisms of phot. sensitivity, London, 1951, p. 297.
4. A. Dainton, A. Gattiker, W. Lock, Phil. Mag. 42, 396 (1951).
5. K. Dixit, J. Sci. Ind. Res. 11, No. 9, 351 (1952).